MEMS microphones are used in a growing number of devices, such as mobile telephones, laptop computers, voice recorders, hearing instruments, and other electronic devices. To those ends, MEMS microphone dies typically are mounted within a package interior and controlled by an adjacent integrated circuit die. For example, a MEMS microphone package may include a substrate, such as an FR-4 based printed circuit board (PCB), a MEMS microphone die attached to the substrate, and a cup-shaped lid attached to the substrate to create a package. The interior of the package forms an interior chamber that protects the fragile MEMS microphone die from the environment.
The interior chamber is not completely isolated, however, from the external environment. Specifically, the package also has an aperture to permit communication between the microphone die and an acoustic signal generated outside of the package. For example, to permit access of an acoustic signal into the package, the substrate may form a through-hole aperture under the microphone die. The acoustic signal thus enters through the aperture, and strikes the diaphragm portion of the microphone die, causing the die to generate corresponding electrical signals.
Ergonomic considerations of an underlying device (e.g., a hearing instrument) often can cause the microphone aperture to be located in a region or wall with very little clearance. The art has responded to this by locating some microphone package apertures in the smaller side walls of the package. Use of the side wall for the aperture, however, can produce an undesirable acoustic path between the hole and the microphone die.